02-05-2008, 03:47 PM
Hi
I am working on a Philco 41-250. You can see the schematic here: http://www.nostalgiaair.org/Resources/407/M0013407.htm
I have replaced all of the rubber wiring. I was not able to test the radio before replacing the wiring due to the many exposed bare wires.
I now have multiple oscillator problems.
First, the oscillator does not oscillate on the AM band, either using the pushbuttons or tuning cap. On the shortwave bands, it would only oscillate for a portion of the range of the tuning cap. After checking the tuning cap for shorts and not finding any, I found that terminal 6 on the oscillator coil was open. It appears that someone had worked on that terminal before as the wire was not rubber coated. I got that fixed.
Now, the oscillator will operate on both shortwave bands for the full range of the tuning cap, but still no AM.
The frequency range for the oscillator on the SW bands is wrong:
SW1: 2.5-5.6 MHz
SW2: 7.5- 8.8 MHz
I found that cap 25 (from the grid of the oscillator tube to the oscillator coil) had been previously replaced). The cap was color coded green, orange, green, which makes no sense to me.(How do you read this color code?) It does however measure 288 pf. I replaced it anyway with a new 270pF for good measure since I didn't have a 250.
Now, the same symptom: no oscillations on AM either from pushbuttons or tuning cap.
I then did some more checking of the wiring. All resistors are in tolerance. The other windings on the oscillator coil are good.
I found that there was a wire running from the top of the variable capacitor which connects to terminal C9 on the wafer switch. This makes no sense at all as the schematic shows terminal C9 going to cap 9 (which in turn goes to the antenna). Also from researching this on the Internet, it appears that the wire going to the top of the tuning cap is suppose to be a "gimmick" cap, a very short piece of wire that is suppose to be fed thru the hole on the other half of the tuning cap and then bent back. On this radio that wire was fed through the hole but was then fed through a hole in the chassis and ran to the wafer switch. BTW, this wire was not rubber coated and falling apart, so obviously it was newer.
The question is? Did someone modify this radio? Did it ever work after being modded? I removed the long wire that went from the tuning cap to terminal C9 on the wafer switch and just put a short one on. I ran it through the other tuning caps lug and then bent it in a "U" shape. This made no difference in my symptom.
Does anyone have a pix of what the gimmick is supposed to look like? Did they all have this gimmick or was their different versions?
Any other suggestions on this radio?
BTW, I swapped the XXL tubes, no change. When oscillating the oscillator tube has -2.2V on the grid and the plate is 33V. When not oscillating the grid is OV.
Thanks
I am working on a Philco 41-250. You can see the schematic here: http://www.nostalgiaair.org/Resources/407/M0013407.htm
I have replaced all of the rubber wiring. I was not able to test the radio before replacing the wiring due to the many exposed bare wires.
I now have multiple oscillator problems.
First, the oscillator does not oscillate on the AM band, either using the pushbuttons or tuning cap. On the shortwave bands, it would only oscillate for a portion of the range of the tuning cap. After checking the tuning cap for shorts and not finding any, I found that terminal 6 on the oscillator coil was open. It appears that someone had worked on that terminal before as the wire was not rubber coated. I got that fixed.
Now, the oscillator will operate on both shortwave bands for the full range of the tuning cap, but still no AM.
The frequency range for the oscillator on the SW bands is wrong:
SW1: 2.5-5.6 MHz
SW2: 7.5- 8.8 MHz
I found that cap 25 (from the grid of the oscillator tube to the oscillator coil) had been previously replaced). The cap was color coded green, orange, green, which makes no sense to me.(How do you read this color code?) It does however measure 288 pf. I replaced it anyway with a new 270pF for good measure since I didn't have a 250.
Now, the same symptom: no oscillations on AM either from pushbuttons or tuning cap.
I then did some more checking of the wiring. All resistors are in tolerance. The other windings on the oscillator coil are good.
I found that there was a wire running from the top of the variable capacitor which connects to terminal C9 on the wafer switch. This makes no sense at all as the schematic shows terminal C9 going to cap 9 (which in turn goes to the antenna). Also from researching this on the Internet, it appears that the wire going to the top of the tuning cap is suppose to be a "gimmick" cap, a very short piece of wire that is suppose to be fed thru the hole on the other half of the tuning cap and then bent back. On this radio that wire was fed through the hole but was then fed through a hole in the chassis and ran to the wafer switch. BTW, this wire was not rubber coated and falling apart, so obviously it was newer.
The question is? Did someone modify this radio? Did it ever work after being modded? I removed the long wire that went from the tuning cap to terminal C9 on the wafer switch and just put a short one on. I ran it through the other tuning caps lug and then bent it in a "U" shape. This made no difference in my symptom.
Does anyone have a pix of what the gimmick is supposed to look like? Did they all have this gimmick or was their different versions?
Any other suggestions on this radio?
BTW, I swapped the XXL tubes, no change. When oscillating the oscillator tube has -2.2V on the grid and the plate is 33V. When not oscillating the grid is OV.
Thanks